1. Field of the Invention
The present invention relates to a liquid crystal display device of a "chip-on-glass" (hereinafter referred to as "COG") type or "chip-on-film" (hereinafter referred to as "COF") type in which a semiconductor chip is directly mounted on a wiring pattern on a substrate of e.g. glass constituting a liquid crystal panel, or on a film substrate connected directly or through a heat seal to a liquid crystal panel. The present invention is more particularly to a liquid crystal display device capable of making the connecting pressure between each of electrodes pads of the semiconductor chip and a wiring pattern constant so that uniform electric connection therebetween can be obtained.
2. Description of the Related Art
In a liquid crystal display (LC) device, transparent electrode patterns are formed respectively on two glass substrates so that they are opposite to and spaced from each other by a prescribed interval, and a liquid crystal material is sandwiched therebetween. A data signal is supplied to each of segment electrodes (pixel electrodes) so that each segment electrode is on/off controlled to provide a desired display. Traditionally, supply of the data signal to each segment electrode was made in such a manner that each segment electrode is connected to a circuit board and the data signal is directly supplied from a signal processing circuit provided on the circuit board to each segment electrode.
However, an increase in the number of segment electrodes leads to a great increase in the number of connecting wirings. Therefore, in recent years, a COG type display device is used in which a semiconductor chip (IC chip) for signal processing is directly mounted on a glass substrate, or a COF type display device is used in which the IC chip is directly mounted on a wiring pattern of a film substrate electrically connected to a liquid crystal panel.
Meanwhile, FIG. 6A is a plan view of a connection portion between a part of an IC chip 2 and wiring patterns 5. As seen from FIG. 4, the interval A between the wiring patterns 5 is as narrow as 50-100 .mu.m. For this reason, the electric connection between the IC chip and wiring pattern of the COG type and COF type display devices is made by thermal crimping technique. In this technique, as seen from the section shown in FIG. 6B, anisotropic conductive adhesive 6 is applied or labelled on the wiring pattern 5 on the film substrate 4, the IC chip 2 is pressed thereon with constant force F while heating (by thermal compression bonding method), and the adhesive is hardened. The anisotropic conductive adhesive 6 is composed of epoxy resin mixed with metallic conductive particles 6a. When the adhesive 6 is pressed by fixed force, the epoxy resin is extruded in a lateral direction. Since the conductive particles 6a are sandwiched between an electrode pad 3 of the IC chip 2 and the wiring pattern 5, the electrode pad 3 and the wiring pattern 5 are electrically connected to each other. On the other hand, in the lateral direction, they are insulated by the epoxy resin.
With a development of the miniaturization and high definition of the liquid crystal display device in recent years, the numbers of output terminals increases and electrode pads of the IC chip 2 to be connected to the wiring patterns 5 have been increased. Where different numbers of the electrode pads 3 are provided on e.g. both opposite sides of the IC chip 2, the electrode pads 3 each having a prescribed width cannot be provided at regular intervals so that there is a tendency for the electrode pads 3 to have different areas. For example, in FIG. 6B, electrode pad C has a large width of 85 .mu.m whereas electrode pad B has a small width of 47 .mu.m. In this case, each wiring of the wiring pattern has a width enough to cover any electrode pad 3. Therefore, the contact area between each electrode pad 3 and each wiring of the wiring pattern 5 is 85 .mu.m (width).times.85 .mu.m (length) for the electrode pad C and 47 .mu.m.times.85 .mu.m for the electrode pad B. The ratio of contact area between the electrode pads C and B is as large as about 9:5, and difference of the contact area between the electrode pads C and B is large.
As described above, where a plurality of electrode pads of the IC chip are provided, there is a tendency for the electrode pads to have different areas. On the other hand, traditionally, each wiring of the wiring pattern 5 is formed to cover the corresponding electrode pad. Therefore, as the case may be, the areas of the electrode pads of the IC chip and the wiring pattern are different according to different electrode pads. The electrode pads and the corresponding wiring patterns are connected by thermal crimping through application of prescribed pressure using anisotropic conductive adhesive of epoxy resin mixed with conductive particles. Therefore, different contact areas lead to different pressures to be applied to the conductive particles to be in contact with each electrode pad. With different pressures, the conductive particles are not sufficiently crushed at the electrode pad to which low pressure is applied, thereby providing insufficient electrical contact and hence poor contact. Such a tendency is particularly remarkable where the IC chip is mounted on a soft flexible film substrate as in the case of COF type display device.
The present invention has been accomplished in order to solve such a problem.